Apparatus and method for determining density of insulation

ABSTRACT

An apparatus for determining the density of insulation in a cavity of a structure that senses a force of the insulation against the sensor. The force is used to determine the density of the insulation, which, in turn, is used to determine the thermal resistance or R-value of the insulation. The apparatus may include a fixture for supporting the sensor and holding the sensor in the substantially fixed position. A method for determining the density of loose-fill, blown-in-place insulation in a wall cavity by the use of a sensor is that measures a force exerted on the sensor by the insulation. The measured force is used to determine the density of the insulation. The thermal resistance of the insulation is determined from the known cavity depth and insulation density.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.10/969,427, filed Oct. 20, 2004, which in turn is a continuation-in-partof U.S. patent application Ser. No. 10/689,770, filed Oct. 21, 2003,each application incorporated herein by reference.

TECHNICAL FIELD AND INDUSTRIAL APPLICABILITY OF THE INVENTION

This invention relates in general to an apparatus and method fordetermining the density of insulation, and in particular, to anapparatus and method for determining the density of a loose-fill,blown-in-place fibrous insulation.

BACKGROUND OF THE INVENTION

In recent years, a greater emphasis has been placed on the use ofinsulation materials in dwellings or other structures to promote energyconservation and noise reduction. At the same time, innovativearchitectural designs have created a variety of shapes and sizes that donot always lend themselves to the use of a conventional fibrous batting,which is often available in rolls of uniform width. This has created aneed for a technique for applying fibrous insulation that does not useuniform width batting.

This need has been fulfilled to a limited extent by developing variousblown-in-place insulation techniques, wherein loose-fill fibrousinsulation is blown into a cavity between the framing members of thewall, ceiling, or floor of a dwelling. The loose-fill insulation isprovides a low cost installation techniques and is perceived as capableof completely filling the cavity, regardless of its shape and size,achieving a uniform volume of insulation for optimum energyconservation, as well as sound insulation purposes.

While blown-in-place insulation techniques provide a low cost method ofinstalling insulation, one of the advantages of batting lost toblown-in-place insulation is the batting's ability to provide apredetermined insulation value, also known as the “R-value”. The R-valuecan be determined by the thickness (T) of the fibrous insulation and theinsulation constant (k) using equation 1.R=T/k  (1)

In the manufacture of fiberglass batts it is a relatively simple matterto determine the nominal thickness and insulation constant to determinethe R-value of the batt. This R-value is then printed on the batt duringmanufacture. When insulation batting is purchased, for example, to placein a new dwelling, it is often purchased by specifying a desiredR-value. If installed in accordance with minimal prescribed installingtechniques, the purchaser, due to uniform dimensions of insulationbatting, can be count on at the insulation value having a certainthermal resistance.

The R-value of blown-in-place insulation is determined by Eq. 1 (above),however k is dependent on the density of the insulation. Therefore, oneadvantage of the easily determined R-value associated with batting istypically not applicable. As a consequence, it is necessary to alsoemploy a secondary technique for determining the density of theblown-in-place insulation for assuring that the insulation has thedesired R-value.

Various secondary techniques have been employed for the determiningdensity in blown-in-place fibrous insulations. In one technique, a knownmass of loose-fill is blown into a cavity of a known volume. The mass isdivided by the cavity volume to determine density and R-value. A problemwith this technique is that it slows down the installation process ofthe insulation and therefore, may not be easily used in the field. It isalso difficult to calculate the actual volume of the cavity becausethere are typically features such as windows, doors, devices in the areathat take up volume. Further, inexperienced insulation installers maynot provide an even volume filling density that causes the density andR-value to vary between cavities.

In another known technique, a space is first filled with blown-in-placeinsulation. Then, a sample of insulation of a known volume is removedfrom a wall cavity and weighed. Using the volume of the sample, it ispossible to determine the density of the insulation in the cavity byweighing the sample and dividing the weight by the known volume. TheR-value of the insulation may then be determined in a known mannersimply by knowing the thickness of the insulation in the cavity. In someinstances, the quantity of insulation may be loose or compressed. As aconsequence, error in determining the density of the insulation can bemagnified if care is not taken to correctly remove the sample or averagea number of samples. This is also a very time consuming technique andconsequently is not preferred by insulation installers.

In yet another known technique, netting is secured to wall studsto.enclose an underlying cavity. Insulation is blown into the cavitythrough a hole in the netting. The netting retains the insulation in thecavity. U.S. Pat. No. 4,712,347 to Henry V. Sperber discloses observingthe bulging out of the netting as a signal that a sufficient amount ofinsulation has been fed into the cavity behind the netting. Thistechnique is unreliable because it is based on the subjectiveobservation of the insulation installers and the tension of the nettingapplied to the cavities. Moreover, the mechanical properties such as themodulus of elasticity of the netting material affect the resiliency ofthe netting and the appearance of the bulge. In addition, the modulus ofelasticity of the insulation, which is affected by the fiber diameterand the presence or absence of a binder, controls the resiliency of theinsulation. Environmental conditions, such as humidity, may also affectthe accuracy of the technique. Another disadvantage of this technique isthat installers, in an effort to insure that a cavity is adequatelyfilled, often overfill the cavity. Overfilling the cavity is undesirablebecause it causes the netting to bulge too much and wastes insulation.If the netting bulges too much, wallboard is difficult to install on theframing members. This has been recognized as a problem and thus has ledto the use of a shield during installation, whereby the shield is heldagainst the netting while the cavity is being filled to prevent thenetting from bulging undesirably.

In view of the above techniques, it is apparent that there exists a needin the art for an improved apparatus and method for installinginsulation that is blown into open wall cavities to a prescribed densitywherein the improved apparatus and method provide increased accuracy.

SUMMARY OF THE INVENTION

The above objects, as well as other objects not specifically enumerated,are achieved by an apparatus for determining the density of insulationin a cavity of a dwelling or other structure. The apparatus is in theform of a sensor that is held within the cavity of the structure andrelative to the insulation in the cavity for sensing the force of theinsulation against the sensor. The force is used to determine thedensity of the insulation, which, in turn, is used to determine thethermal resistance or R-value of the insulation.

An alternative apparatus includes a sensor and a fixture supporting thesensor. The fixture is structured and dimensioned to hold the sensoragainst the insulation within the cavity to measure a material propertyof the insulation and therefore determine density and R-value. Thematerial property may be resistance to an applied force, pressure withinthe cavity, resistance to air flow, or any other material property thatmay be used effectively to calculate density or R-value.

A method for determining the density of loose-fill, blown-in-placeinsulation comprises the initial step of providing a structure thatincludes framing members and a sheath forming at least one cavity havinga known depth. An exposed side of the cavity is covered with netting.The cavity is then filled with insulation. A sensor is held in contactwith the netting or the insulation in the cavity. The sensor thendetects a material property of the insulation that may be converted to adensity or R-value. For example, a force may be exerted by the sensor onthe insulation. The force may include mechanical force, air pressuredifferential, ultra-sonic response or any other force that may be usedto calculate density. The thermal resistance of the insulation isdetermined from the known cavity depth and insulation density.

Various objects and advantages of this invention will become apparent tothose skilled in the art from the following detailed description of thepreferred embodiment, when read in light of the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a diagrammatic representation in plan of a partial structureof a dwelling or other structure.

FIG. 2 is a schematic representation in plan of an apparatus fordetermining the density of a loose-fill, blown-in-place fibrousinsulation in a cavity of the structure illustrated in FIG. 1.

FIGS. 3A and 3B are diagrammatic representations in plan of sensors ofthe apparatus according to the invention supported within the cavity ofthe structure illustrated in FIG. 1.

FIG. 4 is a schematic representation in plan of a fixture for supportinga sensor according to the invention outside the cavity.

FIG. 5 is a diagrammatic representation in plan of a fixture accordingto one embodiment of the invention.

FIG. 6 is a diagrammatic representation in plan of a fixture accordingto another embodiment of the invention.

FIG. 7 is a diagrammatic representation in plan of a fixture accordingto yet another embodiment of the invention.

FIG. 8 is a diagrammatic representation in plan of a sensor according toone embodiment of the invention.

FIG. 9 is a diagrammatic representation in plan of a sensor according toanother embodiment of the invention.

FIG. 10 is a block diagram of a method for determining the density of aloose-fill, blown-in-place fibrous insulation.

FIG. 11 is graph of empirical data relating to the relationship betweenthe density and the spring force of the loose-fill insulation and apolynomial used in a regression to arrive at the empirical data.

FIG. 12 is graph of empirical data relating to the relationship betweenthe density and the pressure drop through the loose-fill insulation anda polynomial used in a regression to arrive at the empirical data.

DETAILED DESCRIPTION AND PREFERED EMBODIMENTS OF THE INVENTION

Referring now to the drawings, there is illustrated in FIG. 1 a partialstructure of a dwelling or other building structure, indicated generallyat 10, including framing members 12, such as wall studs, ceiling joists,or floor joists. Various other framing members, not shown, the purposeof which will be apparent to those skilled in the art, maybe included inthe structure 10. A cavity 14 is formed between the framing members 12.An inner side of the cavity 14 is covered with a sheet or netting 16. Anouter side of the cavity 14 is covered with an exterior sheathing 18,which sheathes the structure 10 except at locations of doors andwindows, not shown.

Insulation 20 is installed in the cavity 14 to prevent heat passageeither outwardly or inwardly through the structure, and to minimizesound transmission therethrough. The insulation 20 is preferably aloose-fill, blown-in-place fibrous insulation. The insulation 20 mayconsist of any suitable material useful for insulation purposes. Suchinsulation 20 may be installed in a conventional manner, such as throughuse of a blower apparatus, not shown, which picks up the insulation inan air stream and carries the insulation to the cavity 14 through a tubeor hose, also not shown.

The netting 16 is preferably relatively thin, yet are capable ofcontaining the insulation 20 in the cavity 14 to hold the insulation 20in place, and serves to permit air to escape from the cavity 14 whilefilling the cavity 14 with insulation 20. The netting 16 terminates atlower and upper ends of the cavity 14 at framing members, such as a sillplate and a header, not shown, that traverse the framing members 12.

An apparatus for determining the density of insulation 20 in the cavity14 is schematically represented at 30 in FIG. 2. The determination ofdensity leads to the determination of thermal resistance, or theR-value, of the insulation 20. The apparatus 30 comprises a sensor 32that is adapted to be held in a substantially fixed position relative tothe insulation 20 in the cavity 14. The term “substantially” withrespect to the term “fixed” means that the sensor 32 will be held in aposition relative to the insulation that allows reliable densitydeterminations to be repeatedly made by the sensor 32. That is to say,the sensor 32 may suffer some minor deviation in position as long as thedensity determinations remain reliable.

According to the present invention, the sensor 32 senses force F, or achange in force, which is used to determine density, as will bedescribed in greater detail in the description hereinbelow. Numerousembodiments of the apparatus 30 can be used to carry out the invention.Some examples of such embodiments are set forth in the followingparagraphs.

In one embodiment of the invention, the sensor 32 is supported withinthe cavity 14. This may be accomplished by attaching the sensors to thesheathing 18 or the netting 16, as shown in FIGS. 3A or 3B. When theinsulation 20 is blown into the cavity 14, the sensor 32 senses theforce F of the insulation. In accordance with this embodiment, ameasurement of force F may be taken from within the cavity 14 via aphysical or wireless connection, not shown, by the sensor 32.

In another embodiment of the invention, the sensor 32 is supportedagainst the netting 16 and the insulation 20 but is located outside thecavity 14. This can be accomplished in any suitable manner. For example,a fixture 34 could be provided for supporting the sensor 32, asschematically illustrated in FIG. 4. The fixture 34 can be any suitablestructure that is adapted to hold the sensor 32 in a substantially fixedposition relative to the insulation 20.

In FIG. 5, there is illustrated a fixture in the form of a standard 36that may be supported by a supporting surface 22 adjacent the cavity 14with the insulation 20 therein. The sensor 32 is adapted to be supportedby the standard 36 in a manner so that the sensor 32 can be repeatedlyheld in a fixed position relative to the netting 16 and the insulation20. For example, the standard 36 may include a foot 38 for establishinga set distance for the standard 36 away from the netting 16 and theinsulation 20.

In FIG. 6, there is illustrated a fixture in the form of a plate 40 thatis adapted to be repeatedly held in a fixed position relative to thenetting 16 and the insulation 20. The plate 40 can be held in contactwith the netting 16 and the insulation 20, or, as shown in FIG. 6,spaced from the netting 16 and the insulation 20, as long as theposition is substantially consistent to permit correlated determinationsof density to be made. In the illustrated embodiment, the plate 40 isadapted to be held a fixed distance D from the netting 16 and theinsulation 20 in the cavity 14 with each determination of density madeby the apparatus. This can be accomplished with legs 42 that extend fromthe plate 40 to engage the framing members 12, although such is notrequired. The distance D is preferably a distance whereby the sensor 32does not extend beyond a plane P that is coplanar with the inner sidesof the framing members 12, or into the cavity 14 between the framingmembers 12.

In FIG. 7, there is illustrated another fixture, which is also in theform of a plate 40. Extending from the plate 40 are pins 44 that areadapted to pierce the netting 16, pass through the insulation 20 in thecavity 14 without substantially affecting its density, and engage theinner side of the sheath 18. The length L of the pins 44 may be fixed oradjustable to accommodate framing members 12 having differentdimensions. For example, the length L of the pins 44 may beapproximately 3½ inches in length if the framing members 12 are nominal2×4 studs or approximately 5½ inches in length if the framing members 12are nominal 2×6 ceiling joists. Adjustment of the pins 44 may beaccomplished in any suitable manner, such as, for example, providingapertures, not shown, through the plate 40 and a clamp 46 in fixedposition relative to the plate 40 and in alignment with the apertures.The pins 44 may pass through the apertures and the clamps 46 may securethe pins 44 in a desired position relative to the plate 40.Alternatively, the pins 44 may be telescopically adjustable, oradjustable in some other suitable manner.

The sensor 32 according to one embodiment of the invention may be in theform of a load cell for measuring the force of the insulation 20 in thecavity 14. Such a sensor 32 would be suitable for use within or outsidethe cavity 14, as schematically represented in FIGS. 2 and 4, or in anyof the embodiments of the invention described herein. Any conventionalload cell may be suitable for carrying out the invention.

In FIG. 8, there is illustrated a sensor in the form of a forcetransducer 48. The force transducer 48 is adapted to measure the force Fencountered by a contact plate 50 held against the insulation 20. Theforce transducer 48 may be a digital transducer or an analog transducer.The force transducer 48 can be held in a fixed relation to theinsulation 20 in any suitable, such as with the use of any of thefixture 52 shown, or any of the fixtures described above. Alternatively,an analog spring-force meter may be used in the place of the forcetransducer 48. In accordance with the invention, the insulation 20 willexert a force F against the force transducer 48, and that force F willbe directly related to the density of the insulation 20.

In FIG. 9, there is illustrated another embodiment of a sensor in theform of an air cup 54. The air cup 54 includes a contact surface 60. Thecontact surface 60 is configured to press against the netting 16 and theinsulation 20 in the cavity 14 behind the netting 16. As shown in FIG.9, the air cup 54 can be mounted to an air cup fixture 62. The air cupfixture 62 is configured to support the air cup 54 and hold the air cup54 in a fixed position relative to the netting 16 and the insulation 20.In the embodiment shown in FIG. 9, the air cup fixture 62 includes anair cup plate 64 and a plurality of air cup legs 66, similar to theplate 40 and legs 42 as shown in FIG. 6. In another embodiment, the aircup fixture 62 could be any suitable structure configured to support theair cup 54 and hold the air cup 54, such as for example, the fixture 36shown in FIG. 7. In the embodiment shown in FIG. 9, the air cup fixture62 is mounted to framing members 12, although other mounting methodscould be used. In yet another embodiment, the air cup fixture 62 couldbe a free standing structure, such as for example, the fixture 36 shownin FIG. 5. As previously mentioned, the contact surface 60 is configuredto press against the netting 16 thereby forming a hollow space 68 withinthe air cup 54. A pressure differential between the air cup 54 and theatmosphere is created within the air cup 54. The pressure differentialmay be produced by introducing air, through a source connector 67 a,into the air cup 54 from a pressure device 56. The pressure device 56may be in the form of an air tank, an air pump or any other suitabledevice to increase the pressure within the air cup 54. Similarly, airmay be evacuated from the air cup 54 by an air pump, a vacuum, or anyother suitable device to decrease the pressure within the air cup 54. Asfurther shown in FIG. 9, a gauge 58 is connected to the air cup 54 by aconnector 67 b. The qauge 58 is configured to determine the air pressuredifferential between the air cup 54 and the atmosphere. The gauge 58 isconfigured to determine the density of the insulation from the airpressure differential by, for example, using a predetermined equationproviding the relationship between the air pressure differential and thedensity of the insulation 20. The pressure in the air cup 54 will bedirectly related to the density of the insulation 20 behind the netting16.

In FIG. 10 there is illustrated a method for determining the density ofloose-fill, blown-in-place insulation in a cavity defined betweenframing members of a dwelling or other structure. A method according toa preferred embodiment of the invention may comprise an initial step 110of providing a structure having framing members and a sheath forming atleast one cavity having a known depth of thickness. In step 112, aninner side of the cavity is covered with netting. In step 114, thecavity is filled with insulation. The insulation is preferably aloose-fill, blown-in-place fibrous insulation. The netting is preferablycapable of containing the insulation in the cavity while permitting airto escape from the cavity while the cavity is filled with insulation.

In a subsequent step 116, a sensor is held in a substantially fixedposition relative to the insulation in the cavity. In step 118, thesensor measures force exerted on the sensor by the insulation. In step120, the force is used to determine the density of the insulation. Instep 122, the thermal resistance of the insulation is determined fromthe known cavity depth and insulation density.

In optional step 124, the sensor is supported within the cavity. Thesensor may be attached to the netting or the sheathing prior to fillingthe cavity with the insulation. When the insulation is blown into thecavity, the sensor senses the force exerted against the sensor by theinsulation.

In an alternative step 126, a fixture is provided for supporting thesensor outside the cavity and holding the sensor in a substantiallyfixed position relative to the netting and the insulation. The fixturemay be in the form of a standard supported by a supporting surfaceadjacent the cavity and the insulation therein. Alternatively, thefixture may be in the form of a plate that holds the sensor against thenetting and insulation. The plate could be held a distance from theframing members by legs that engage the framing members. Alternatively,the plate could be held a distance from the sheathing by pins that passthrough the netting and the insulation and engage the sheathing. Thepins could be adjusted in length to accommodate framing members havingdifferent dimensions.

The sensor of step 116 may be in the form of a load cell that senses theforce of the insulation against the sensor. Alternatively, the sensormay be a digital or analog force transducer. The.transducer can be heldin a fixed position relative to the insulation with the fixture providedin step 126. A spring-force meter may be used in the place of thetransducer. Alternatively, the sensor may be in the form of an air cupthat is pressed against the netting and insulation. It will beappreciated that if the sensor provided in step 116 is an air cup, thenan optional step 128 may be performed in which a pressure differentialbetween the air cup and the atmosphere. In step 118, the force exertedis then determined by measuring the air pressure in the air cup, such asby using a gauge. The pressure in the air cup is directly related to thedensity of the insulation behind the netting.

The aforementioned force transducer 48 and spring-force meter rely onthe natural spring force of the loose-fill insulation to gage density.As the density of loose-fill insulation increases, the spring forceincreases proportionally. Using polynomial regression, an empiricalrelationship can be found between the density and the spring force ofthe loose-fill insulation. An example of a polynomial and empirical datarelating to the relationship between the density and the spring forcefor is shown in FIG. 11.

The embodiment of the apparatus or method that uses the air cup relieson the natural resistance to flow of the loose-fill insulation to createa pressure drop. For a given source pressure, the loose-fill insulationhas a characteristic pressure drop for a given density. Further, backpressure created on the high-pressure side of the loose-fill insulationis directly proportional to density. Using polynomial regression, anempirical relationship can be found between the density and pressuredrop. An example of a polynomial and empirical data relating to therelationship between the density and the pressure drop through theinsulation is shown in FIG. 12.

Factors that can affect either embodiment of the invention include themorphology, diameter, characteristic length, and shape of the fibers ofthe insulation factors, the binder content, if a binder is used, andother factors that are not mentioned.

The loose-fill thermal conductance, which is inversely proportionate tothermal resistance, can be related to the density by laboratory testing.The data can then curve fitted, as shown in FIGS. 11, and 12.

The invention of this application has been described above bothgenerically and with regard to specific embodiments. Although theinvention has been set forth in what is believed to be the preferredembodiments, a wide variety of alternatives known to those of skill inthe art can be selected within the generic disclosure. The invention isnot otherwise limited, except for the recitation of the claims set forthbelow.

1. A method for conducting an on-site measurement of the density or R-value of insulation material using an apparatus comprising a chamber comprising a first fluid passageway and a second fluid passageway, wherein the first fluid passageway is in fluid communication with the second fluid passageway via the chamber; and wherein the second fluid passageway is configured to engage the insulation material and to convey a gas flow to or from the insulation material; and a sensor arranged to measure the pressure in the chamber; said method comprising: measuring the pressure in the chamber while a gas flow is not being introduced into the chamber to obtain a first pressure measurement; positioning the second fluid passageway proximal to or in contact with the insulation material; introducing a gas flow into the chamber; measuring the pressure in the chamber while the gas flow is being introduced into the chamber to obtain a second pressure measurement; and determining a pressure differential based on the first and second pressure measurements.
 2. The method of claim 1, further comprising a step of correlating the pressure differential to the density or R-value of insulation material.
 3. The method of claim 1, wherein the step of introducing a gas flow into the chamber includes connecting first fluid passageway to a flow of gas from a gas source:
 4. The method of claim 3, wherein the gas source is compressed air.
 5. A method for conducting an on-site measurement of the density or R-value of insulation material using an apparatus comprising: a chamber comprising a first fluid passageway and a second fluid passageway, wherein the first fluid passageway is in fluid communication with the second fluid passageway via the chamber: and wherein the second fluid passageway is configured to engage the insulation material and to convey a gas flow to or from the insulation material; and a sensor arranged to measure the pressure in the chamber and adapted to determine the density of the insulation material based on measurements obtained by the sensor; said method comprising: measuring the pressure in the chamber while a gas flow is not being introduced into the chamber to obtain a first pressure measurement; positioning the second fluid passageway proximal to or in contact with the insulation material; introducing a gas flow into the chamber; measuring the pressure in the chamber while the gas flow is being introduced into the chamber to obtain a second pressure measurement; determining a pressure differential based on the first and second pressure measurements; and determining the density of the insulation material based on the pressure differential.
 6. The method of claim 5, wherein the step of introducing a gas flow into the chamber includes connecting first fluid passageway to a flow of gas from a gas source.
 7. The method of claim 6, wherein the gas source is compressed air.
 8. A system suitable for conducting an on-site measurement of the density and/or R-value of insulation material in a building structure, comprising: a building structure having framing members, wherein an insulation cavity is formed between adjacent framing members; insulation material disposed within the insulation cavity; netting attached to the building structure and containing the insulation material within the insulation cavity; and an apparatus for conducting an on-site measurement of the density and/or R-value of the insulation material, comprising: a chamber comprising a first fluid passageway and a second fluid passageway, wherein the first fluid passageway is in fluid communication with the second fluid passageway via the chamber; wherein the second fluid passageway is positioned against the netting and is further configured to convey a gas flow through the netting to or from the insulation material in the insulation cavity; and a sensor arranged to measure the pressure in the chamber.
 9. The system of claim 8, wherein the sensor is adapted to determine a pressure drop.
 10. The system of claim 8, wherein the sensor is adapted to determine a first pressure and a second pressure and a pressure differential.
 11. The system of claim 8, further comprising a source of gas in fluid communication with the first fluid passageway for introducing a gas flow into the chamber.
 12. The system of claim 11, wherein the source of gas is compressed air. 